I have been experimenting with my V60 brews lately. I am logging TDS (estimated with a cheap-o Brix meter) and extraction (using formula from coffeeadastra), and seem to be getting somewhat low extraction yields at around 18-19%. I have tried a couple of things - tested several techniques (continuous pour/pulsing, stirring etc), grind sizes (decreased it as far as I could down in grind size - extraction was stable until it suddenly crashed, probably due to channeling) etc. However, finally I adjusted my coffee:water ratio to 1:18.5 instead of <1:17 I usually used before - and voilá, I am getting TDS of 1.32 and extraction at around 21.6%. To me it seems rather tasty, and TDS-wise it appears to match nicely a very respectable coffee chain in my city (they do pour-overs on a Kalita) whose coffee gives me a tad higher TDS (1.36).

So, my question is, 1:18.5 seems a bit high - is that a reflection of uneven grind?